The invention relates to the field of transmissions, and more specifically, a system for and method of shifting a transmission to maximize fuel economy.
Transmissions control gear ratio changes in accordance with a shift map. Transmission designs may incorporate an automatic shifting mode known as xe2x80x9cConstant Groundspeed Autoshiftxe2x80x9d (CGA mode), which will automatically shift the transmission to maintain a desired groundspeed. An examination of a transmission system operating in CGA mode reveals that, for any given groundspeed command, the transmission gear ratio requirement is not unique. In other words, any one of several different combinations of engine speed and transmission gear ratio will produce the desired groundspeed. Because of this inherent flexibility, a transmission system can be designed to select the appropriate engine speed and transmission gear ratio based on a selected criterion. It would be useful to select the preferred gear ratio based on maximizing fuel economy, while maintaining an operator""s selected groundspeed.
A transmission which attempts to maximize fuel economy in a continuously variable transmission is disclosed in U.S. Pat. No. 4,594,666, xe2x80x9cTransmission Monitor/Control Microprocessor for Continuously Variable Power Trainxe2x80x9d. This patent describes a method for controlling a variable ratio power train to automatically adjust the drive reduction ratio so that engine power at all levels is produced at a minimum brake-specific fuel consumption (BSFC). However, the patent only discloses use of such a system with a continuously variable transmission, not with a standard step gear system. The disclosed embodiment of the invention is for a CVT system having operator adjusted HI, MID, and LO range settings, settings which the operator must adjust or the invention cannot maintain adequate power. In addition, the invention does not teach allowing the operator to set a desired groundspeed while maintaining a minimum fuel use; rather, the invention teaches the operator setting a desired power level that the system attempts to maintain, regardless of groundspeed.
The present invention is directed to overcoming one or more problems or disadvantages associated with the prior art.
In accordance with an aspect of the present invention, a method of determining shift points in a step gear transmission system to maximize fuel economy is disclosed. In operation, the method uses fuel economy data from a first gear ratio to determine a first series of constant fuel consumption curves for the first gear ratio. The method then uses fuel economy data from a second gear ratio to determine a second series of constant fuel consumption curves for the second gear ratio. Next, the method determines points of intersection where a respective fuel consumption curve for the first gear ratio intersects its corresponding fuel consumption curve for the second gear ratio. A decision curve is generated from the points of intersection.
In accordance with another aspect of the present invention, a machine-readable storage medium having stored thereon machine executable instructions is disclosed. The execution of the instructions is adapted to implement a method for determining shift points in a step gear transmission system to maximize fuel economy. In operation, the method uses fuel economy data from a first gear ratio to determine a first series of constant fuel consumption curves for the first gear ratio. The method then uses fuel economy data from a second gear ratio to determine a second series of constant fuel consumption curves for the second gear ratio. Next, the method determines points of intersection where a respective fuel consumption curve for the first gear ratio intersects its corresponding fuel consumption curve for the second gear ratio. A decision curve is generated from the points of intersection.
In accordance with another aspect of the present invention, a system for determining shift points in a step gear transmission system to maximize fuel economy is disclosed. The system includes a controller and memory coupled to the controller. The controller is operable to use fuel economy data from a first gear ratio to determine a first series of constant fuel consumption curves for the first gear ratio. The controller then uses fuel economy data from a second gear ratio to determine a second series of constant fuel consumption curves for the second gear ratio. Next, the controller determines points of intersection where a respective fuel consumption curve for the first gear ratio intersects its corresponding fuel consumption curve for the second gear ratio. A decision curve is generated from the points of intersection.
In accordance with another aspect of the present invention, a method of controlling a step gear transmission to maximize fuel economy is disclosed. The method receives data regarding the operating point of the engine. The operating point is compared to a stored decision curve, wherein the decision curve divides a range of operating points between a first adjacent gear ratio and a second adjacent gear ratio based on the most fuel efficient gear ratio for operation. The method includes shifting the transmission between the first adjacent gear ratio and the second adjacent gear ratio based on the comparison of the operating point to the decision curve.
In accordance with another aspect of the present invention, a system for controlling a step gear transmission to maximize fuel economy is disclosed. The system includes a controller and memory coupled to the controller. The controller receives data regarding the operating point of the engine. The operating point is compared to a stored decision curve, wherein the decision curve divides a range of operating points between a first adjacent gear ratio and a second adjacent gear ratio based on the most fuel efficient gear ratio for operation. The method includes shifting the transmission between the first adjacent gear ratio and the second adjacent gear ratio based on the comparison of the operating point to the decision curve.
The foregoing summarizes only a few aspects of the invention and is not intended to be reflective of the full scope of the invention as claimed. Additional features and advantages of the invention are set. forth in the following description, may be apparent from the description, or may be learned by practicing the invention. Moreover, both the foregoing summary and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.